SCIENTIFIC HIGHLIGHTS

Storing information in a ferromagnetic insulating barrier

Magnetic anisotropy converts a tunnel junction device, in which the only magnetic material is the barrier, into a memory device

Multiple spin functionalities are tested on Pt/La2Co0.8Mn1.2O6/Nb:SrTiO3, a device composed by a ferromagnetic insulating (FMI) barrier sandwiched between nonmagnetic electrodes. FMIs are scarce in nature, as ferromagnetic interactions are typically of exchange-type mediated by charge carriers, and they can play an important role in spintronics as an efficient way to obtain polarized currents when used as spin filters. In our device, the only magnetic element is La2Co0.8Mn1.2O6 barrier. Moreover, La2Co0.8Mn1.2O6 thin films present strong perpendicular magnetic anisotropy whose origin lies in the large spin-orbit interaction of Co2+which is additionally tuned by the strain of the crystal lattice.[1] This anisotropy is largely reflected in the transport properties of the junction presenting tunneling anisotropic magnetoresistance (TAMR) values up to 30% at low temperatures, in addition to an estimated spin filtering efficiency of 99.7%.[2] These results are corroborated by DFT-based calculations. We demonstrate that the DOS of La2CoMnO6 has a fully polarized spin-down character above the Fermi level. On the other hand, our calculations estimate a difference in the tunnel barrier height of 8 meV when magnetization changes from OOP to IP, and an exchange splitting of 0.2 eV, in good agreement with values fitted experimentally. Furthermore, we found that the junction can operate as an electrically readable magnetic memory device. Our results probe the existence of a non-volatile bistable resistive state that can be switched by applying magnetic field pulses in perpendicular or parallel directions. Thus, the findings of this work demonstrate that a single ferromagnetic insulating barrier with strong magnetocrystalline anisotropy is sufficient for realizing sensor and memory functionalities in a tunneling device based on TAMR.

Authors:
Laura López-Mir,1 Carlos Frontera,1 Hugo Aramberri,1 Karim Bouzehouane,2 Jose Cisneros-Fernández,1 Bernat Bozzo,1 Lluís Balcells,1 Benjamin Martínez1

Affiliation:
1Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
2Unité Mixte de Physique, CNRS-Thales, France

Publication:
Anisotropic sensor and memory device with a ferromagnetic tunnel barrier as the only magnetic element
Scientific Reports, 8, 861 (2018) 
DOI: 10.1038/s41598-017-19129-5

References in the text:
[1] L. López-Mir, R. Galceran, J. Herrero-Martín, B. Bozzo, J. Cisneros-Fernández, E. V. Pannunzio Miner, A. Pomar, L. Balcells, B. Martínez, C. Frontera, Phys. Rev. B 2017, 95, 224434.
[2] L. López-Mir, C. Frontera, H. Aramberri, K. Bouzehouane, J. Cisneros-Fernández, B. Bozzo, L. Balcells, B. Martínez, Sci. Rep. 2018, 8, DOI 10.1038/s41598-017-19129-5.

Figure caption
a) Schematics of the band diagram of our device with forward applied bias V. F0 is the tunneling barrier that splits into F­ and F¯ for spin up and spin down electrons due to i) the exchange splitting D and the effect of the magnetic field (FH).
b) Resistance and TAMR of the sample with respect to the orientation of the applied field (9T): perpendicular plane (OOP) at q=0º, 180º and in plane (IP) for q=90º, 270º.
c) Resistance measured during 300s after applying/releasing a field of 5T OOP (black) and IP (red). Schematic of magnetic field pulses is depicted at the bottom.
d) Long time measurement (10
5 s) of the two resistance states after a 9T pulse IP (red) and OOP (black).

Coordination
Anna May-Masnou This email address is being protected from spambots. You need JavaScript enabled to view it.
Redaction
Anna May-Masnou This email address is being protected from spambots. You need JavaScript enabled to view it.
Web & Graphic Editor
José Antonio Gómez  This email address is being protected from spambots. You need JavaScript enabled to view it.

Webmasters
José Antonio Gómez This email address is being protected from spambots. You need JavaScript enabled to view it.
Albert Moreno     This email address is being protected from spambots. You need JavaScript enabled to view it.
ICMAB